Enrollment in Indianapolis Public Schools ticked up for the first time in at least four years, thanks to deals struck with local charter schools to join the district’s innovation network.

Enrollment counts aren't officially released by the state until next month, but IPS said it recorded nearly 32,000 students during the official count day Sept. 15, making it the state's largest public school district.

This year's count is up close to 1,000 students from the previous academic year — an increase that can be attributed almost entirely to new charter school partners.

A 2014 state law created the innovation network, allowing IPS to partner with charter schools in a system where schools operate autonomously under outside management while still being considered part of the district. IPS can also add schools to the network by converting existing schools to autonomous programs with charter-like operators. The district has mostly used this provision to restart struggling schools.

"We haven’t set a specific target on the number of students or schools that are going to be potentially innovation schools," Superintendent Lewis Ferebee said. "It's a model we utilize when we believe it's in the best interest of a school and community to do so.

"I anticipate that number will likely grow in the future."

The district added three charter high schools and a middle school to its ranks, while converting three existing elementary schools to innovation network schools. School-level enrollment data hasn't been made available yet, but enrollment between the three new charter high schools should account for nearly all of this year's enrollment bump.

Herron High School, one of the state's highest-performing charter high schools joined IPS earlier this year.

It was a coup for the district, which now gets to count the school's high academic performance and the approximately 800 students it enrolls each year. Herron also launched a second iteration of its sought-after college prep program, Riverside High School. Riverside was expected to enroll between 150 and 200 ninth-grade students this year.

The agreement will give Herron and Riverside access to the district’s resources — potentially buildings, services and additional funding — and IPS will get to add high-performing high schools to its portfolio.

Herron will maintain full autonomy, though, in both operations and academics.

It’s a unique arrangement because charter schools typically work independently, outside the auspices of a public school system and compete with public schools for students. But IPS' innovation schools operate as charter schools within the school district — with their own governing boards and without unionized teachers.

Purdue Polytechnic High School launched as a new school in the innovation network this fall, and also expected an inaugural class of around 150 students.

If all three enrolled the number of students expected, they would account for about 1,100 students on IPS' rolls and about one-third of the number of IPS students in charter schools with similar agreements. The number of students in that type of school grew by about 2,000 from last year.

What's less obvious in the district-level data is how the expanding innovation network is impacting enrollment at the district's remaining traditional public schools. It's unclear if the district is actually attracting new students or if its existing students are shifting to charter schools now under the district's umbrella.

A full quarter of IPS students are now attending schools outside of the traditional public school structure.

The number of students in traditional public schools fell by about 3,000 students while those in innovation network schools grew. That shift is due, at least in part, to the conversion of several existing IPS schools to innovation network schools in the last year, including School 47, also known as the Edison School of the Arts; School 42, also known as Elder W. Diggs; and School 15, also known as Thomas D. Gregg.

The innovation network has been controversial to public school advocates who view it as a way to undermine a public education system. It was repeatedly criticized by opponents to the district's new high school plan, which consolidated IPS high schools from seven to just four next year.

"How can the district recommend closing three IPS schools and at the same time discuss opening three innovation charter high schools with the district?” said Andrew Gatza, a former teacher and resident of the IPS district, at a school board meeting over the summer, where the district announced its partnership with Herron High School.

District leaders have contended that charter schools will open, whether they partner or not.

There are at least four more innovation network schools in the pipeline, through the Innovation Network Fellowship, administered by nonprofit The Mind Trust. All would need IPS board approval to join, but two could launch as soon as next fall with two more shooting for fall 2019.